A digital radiation image detector represented by computed radiography (CR) and flat panel detector (FPD) is widely used in diagnostic imaging in hospital and clinic since it can directly obtain digital radiation images and can directly display the images on an image display equipment such as cathode tube and liquid crystal panel. Recently, a FPD utilizing a thin-film transistor (TFT) and a charge-coupled device (CCD) in combination is being popularized.
The FPD comprises a sensor panel (plane light receiving element) in which a light receiving element such as TFT and CCD is arranged two-dimensionally and a radiation image conversion panel in which a phosphor layer for converting radiation into light detectable by a light receiving element is formed on a support. Recently, further improvements of function are being attempted by constituting the phosphor layer in a multilayer manner.
For example, Patent Literature 1 discloses a radiation image conversion panel comprising a sensor panel and a phosphor layer formed on the sensor panel, the radiation image conversion panel having a structure wherein the phosphor layer has a columnar portion formed by groups of columnar crystals formed by columnar growth of phosphors and a non-columnar portion and wherein the non-columnar portion closely contacts with the sensor panel and the columnar portion is formed thereon toward the crystal growth direction.
Patent Literature 2 discloses a radiation image conversion panel comprising a support and a phosphor layer formed on the support, the radiation image conversion panel having a structure wherein the phosphor layer comprises a plurality of columnar crystals in which phosphor crystals are laminated in columnar shape, and wherein the columnar crystals have a columnar structure at the root side fixed on the support and have a structure forming a helical structure thereon.
Patent Literature 3 discloses a radiation image conversion panel comprising a support and a phosphor layer comprising phosphor columnar crystals on the support, wherein the degree of orientation of plane index (200) of the phosphor columnar crystal determined by X-ray diffraction method is from 80 to 100%.
Patent Literatures 1 and 2 are examples of those in which a role of diffuse reflection layer is imparted to a lower layer of a phosphor layer, but it has become understood that a part of the lower layer becomes amorphous resulting in decreasing luminance or affecting the crystallinity and the crystal diameter distribution of the upper columnar crystals which will grow subsequently.
On the other hand, Patent Literature 3 discloses an example in which plane index determined by X-ray diffraction is oriented toward (200) at any position in the film thickness direction, but characteristics such as luminance and MTF and a crystalline state in the very early stage of crystal growth which has a big influence especially on film adhesion have not been mentioned. Evaluation by the average of X-ray diffractions at the position where effective thickness of sample is relatively large and which is about 10 μm to the thickness direction did not lead to sufficient understanding of the important state in the very early stage of crystal growth. Techniques for controlling the very early part of crystal growth is important, and the necessity is increasing.